Tephra Material Research Articles

Extending the mid-18th century eruptive record of the Cordón Caulle Volcanic Complex (40,5° S) through the study of three lake sedimentary sequences

The research focuses on the characterization of a tephra level extracted from sedimentary sequences obtained from three lacustrine environments from the northern Patagonia Andean range to define the volcano of origin. The dating of the tephra level corresponds to the mid-18th century but there is no scientific record nor geological evidence of this event. The sediment sequences were collected from lakes Nahuel Huapi, Moreno Oeste, and Tonček, in northern Patagonia, located downwind from the Cordón Caulle Volcanic Complex (CCVC), the potential source, at 45, 86, and 95 km respectively. These environments are frequently impacted by tephra falls from different sources in the Southern Volcanic Zone. Particle morphology, glass and mineral chemistry, together with textural analysis, provided a detailed characterization of the tephra layer recovered at each site. This characterization allowed the association of the tephra material with the CCVC predominantly, with minor Osorno volcano contributions. Historical records of both volcanic systems included eruptions in the mid-18th century (1759 CE and 1752–1796 CE, respectively). Hence, the characterization and the comparison with historical records of volcanic eruptions let us conclude that the tephra is composed of materials dispersed by CCVC in the nearby lakes, whereas contributions from Osorno volcano are observed in environments to the south of the study site, during the mid-18th century. The study demonstrates the potential of this type of detailed characterization in lake sequences to develop and support increasing research on historical volcanic records, helping to improve the knowledge of the volcanic hazard of a region.

Middle–Upper Pleistocene tephras in the Papua New Guinea highlands

Eighteen Middle–Upper Pleistocene (ca 200 ka) tephra units in the highlands of Papua New Guinea (PNG) are mapped and described. The study area is about 24 000 km2, extending from Tari in the west to Kainantu and the Kassam Pass in the east. It is estimated that at least 75 000 km2 of highland PNG received ≥50 cm tephra from various highland sources, and the total volume would have been well over 300 km3. Total tephra thicknesses near sources are >20 m, with thicknesses of individual units near source ranging from 1–2 to >4 m. Several units were deposited with coarse ash and lapilli basal layers that have been weathered to fine ash and clay sizes. Hagen, Giluwe and Yelia volcanoes are the main sources, with smaller centres near Giluwe and north of Hagen also producing mappable tephra units. One unit (Birip) was erupted about 40 ka, but most of the tephra units are 200 ka and older. Volumes of tephra suggest that many of the eruptions had volcanic explosivity indices of 4–6. On stable bedrock, tephras are present on slopes up to 35°, demonstrating the high stability of the tephra materials. Gaps in the tephra cover coincide with bedrock that weathers to unstable regolith where tephras did not accumulate; the tephra cover thus provides an indicator of bedrock stability. Mapped tephra units provide the potential for correlation of other Quaternary materials and can be used as widespread marker beds. The tephras are also important as the parent material for the dominant agricultural soils in the highlands.

Characteristics of physical properties of the sliding and its surrounding layers in landslides caused by the 2018 Hokkaido Eastern Iburi Earthquake

A 6.6-Mw earthquake struck the Iburi region of Hokkaido, Japan, in 2018, triggering massive landslides. Most of these landslides were shallow and occurred mostly in the Atsuma and Abira towns. Ta-c and Ta-d tephra layers have been found in the Towa landslide at Atsuma from the Tarumai volcano, while Ta-d, En-a, and Spfa-1 tephra layers have been found in the Mizuho landslide at Abira from the Tarumai and Eniwa volcanos, as well as the Shikotsu caldera. Field observations from previous studies revealed that the sliding layers were located in the Ta-d and En-a layers at the Towa and Mizuho landslides, respectively. Unlike previous research on earthquake-induced landslides, which were investigated using mechanical properties, this study investigates the characteristics of physical properties, saturated permeability properties, and content of clay minerals on sliding and surrounding tephra layers. Results from this study reveal that the physical properties of sliding layers from two landslides demonstrated the same characteristics: non-plastic soil with a low density of soil particles, void ratio, and dry density; these characteristics could influence earthquake-induced landslides. It also reveals a relationship between the plasticity chart and the age of tephra materials, including the relationship between the weathering process and density of soil particles and the dissimilarity in characteristics of saturated permeability properties in tephra materials.

The dating and correlation of an eastern Mediterranean lake sediment sequence: a 46–4 ka tephrostratigraphy for Ioannina (NW Greece)

ABSTRACTTerrestrial archives from the Mediterranean have been crucial to expanding our understanding of past environmental variability on a range of timescales. Dating Quaternary sequences in the Mediterranean is, however, often challenging, and age models often have large chronological uncertainties. Tephra deposits can provide crucial age control for detailed environmental reconstructions on sub‐centennial timescales. Here, tephra analysis is undertaken for the first time on a sediment core (I‐08) from Lake Ioannina, northwest Greece, for the interval spanning 46–4 ka bp. Detailed visible and ‘crypto‐’ tephra analysis identifies deposits associated with explosive volcanism at Italian volcanic sources, including Campi Flegrei, Pantelleria, and the Aeolian Islands. We identify two visible tephra layers, the Campanian Ignimbrite (CI/Y‐5; ca. 39.8 ka bp) and Pantelleria Green Tuff (PGT/Y‐6; ca. 45.7 ka), as well as the Holocene Vallone del Gabellotto cryptotephra marker (VG/E‐1; ca. 8.3 ka bp). Evidence for repeated remobilisation and redeposition of CI tephra material is outlined, and the potential mechanisms and effects of sediment reworking in lake environments are examined. Bayesian modelling, which incorporates the new tephra ages with earlier radiocarbon dates, extends the I‐08 core chronology back to ca. 46 ka bp, facilitating direct correlation of the Ioannina sequence to others in the Mediterranean region.

Growth of Grimmia mosses on volcanic tephra: Geoecological processes of biocrust development in Haleakalā crater (Maui, Hawai′i)

This research examines high-elevation biocrusts on volcanic tephra in Haleakalā Crater, Maui, Hawai′i; geomorphic, ecological, and pedological processes are discussed, in order to provide an integrated geoecological view of linkages that have influenced biocrust genesis. The study considers four spatial scales: (i) the landscape scale; (ii) the site scale; (iii) the miniature scale and, (iv) the microscopic scale. (i) Biocrusts grow at ~ 2335 m on a hydrologic basin circumscribed by four cinder cones which contributed tephra materials during eruptions between 11000 and 5000 BP, ~2700 BP, and 970 ± 50 BP. Basin landforms provide multiple clues about past geomorphic processes that have affected crust evolution, including intermittent runoff, which decreased the length of cryptobiosis periods, allowing poikilohydric mosses to gradually expand into dense biocrusts; and widespread frost activity, which caused tephra sorting and extensive slope creep on cinder cones. Ubiquitous signs of current frost disturbance are also found on basin soils. (ii) The study site, located amidst bare volcanic tephra—ash and lapilli—includes mainly two organisms: an acrocarpous moss, Grimmia torquata, and a foliose lichen, Peltigera rufescens. Biocrusts attained 40.23% groundcover;G. torquata was found on 64 undisturbed specimens, and showed 78.3% frequency on 46 sampling plots, whereas P. rufescens grew on 23.4% of specimens. Biocrusts also supported 13 vascular species. The most common were grasses, with 5.6% cover and 67.4% total frequency, including Trisetum glomeratum (47.8%) and Deschampsia nubigena (19.6%); other vascular plants reached just 0.85% combined cover. Tests show 72% of vascular-plant cover was statistically correlated with presence of biocrusts, suggesting these have beneficial—presumably pedological—effects on vascular plant growth. (iii) Biocrust microtopography was characterized by intermingling areas of rolling, 15–35 mm-high, protrusions, and 40–75 mm-high pinnacles. (iv) Soil micromorphology indicated crust growth was probably influenced by a host of genetic processes, including wind abrasion and erosion; aeolian dust deposition; soil desiccation during seasonal wet-dry cycles; rainwash and raindrop impact; diurnal temperature cycles; and bioturbation by burrowing fauna. The interactions among these agents are integrated into an idealized crust developmental sequence during the past few millennia.

A continuous tephrostratigraphic record from the Labrador Sea spanning the last 65 ka

ABSTRACTVolcanic ash preserved in marine sediment sequences is key for independent synchronization of palaeoclimate records within and across different climate archives. Here we present a continuous tephrostratigraphic record from the Labrador Sea, spanning the last 65–5 ka, an area and time period that has not been investigated in detail within the established North Atlantic tephra framework. We investigated marine sediment core GS16‐204‐22CC for increased tephra occurrences and geochemically analysed the major element composition of tephra shards to identify their source volcano(es). In total we observed eight tephra zones, of which five concentration peaks show isochronous features that can be used as independent tie‐points in future studies. The main transport mechanism of tephra shards to the site was near‐instantaneous deposition by drifting of sea ice along the East Greenland Current. Our results show that the Icelandic Veidivötn volcanic system was the dominant source of tephra material, especially between late Marine Isotope Stage (MIS) 4 and early MIS 3. The Veidivötn system generated volcanic eruptions in cycles of ca. 3–5 ka. We speculate that the quantity of tephra delivered to the Labrador Sea was a result of variable Icelandic ice volume and/or changes in the transportation pathway towards the Labrador Sea.

Volcanic ash generation: Effects of componentry, particle size and conduit geometry on size-reduction processes

Grain size distributions (GSD) of pyroclastic materials are the product of processes ranging from primary fragmentation efficiency to tephra transport. As such, a detailed description of their physical and chemical state can provide pivotal information regarding such processes. By constraining the GSD of volcanic deposits one can thereby deliver powerful constraints on the energetics and dynamics of eruptions. In order to do so we must distinguish between two primary controls: 1) fragmentation of magma to tephra, and 2) secondary transport-related processes (such as abrasion and comminution), within the conduit and until deposition of the particles. Variations in particle interactions in the conduit together with conduit geometry, may be major factors in modifying the GSD. As in all physicochemical processes, for eruptive dynamics an experimental basis is an essential element of calibration and quantification. Here, we have conducted the first experimental investigation linking fragmentation and ash production via the influence of 1) particle-componentry and particle-size, and 2) the conduit geometry (constricted versus unconstricted) on the GSD. Rapid decompression experiments with loose tephra material from the fall deposit of Pomici Principali eruption (10.3 ka, Campi Flegrei) have been conducted in an optically transparent setup that enables the optical monitoring of particle dynamics with a high-speed camera. The samples employed can be classified into two main groups; 1) pumices, and 2) dense clasts (including crystals, lava clasts and wall rock fragments). Our results indicate that 1) a conduit diameter constriction (simulating obstacles in the conduit walls) is likely to reduce the average diameter of individual clasts and increase the generation of ash (<63 μm, fine ash); 2) the presence of larger pumice particles in the starting sample results in more efficient ash production; 3) the presence of dense particles is linked to a higher efficiency of size-reduction processes (whereby the presence of crystal-rich pumice appears to have a counterproductive effect). These findings correlate well with existing studies, enabling a general assessment of possible secondary size-reduction processes controlling the GSD of a volcanic deposit. Further, our results also suggest that secondary-generated ash should be considered for hazard assessment and modeling, since increased amounts of ash may affect, e.g., the plume dispersion dynamics, and in turn the area affected by ash deposition.

Magmatic reactivation of the Campi Flegrei volcanic system: insights from the Baia–Fondi di Baia eruption

The Baia–Fondi di Baia was a multi-stage, small-scale eruption which occurred in the western part of the Campi Flegrei caldera at 9525–9696 BP, marking the onset of Epoch 2 of post-Neapolitan Yellow Tuff volcanism. The eruption was characterized by a complex series of events related to two distinct eruptive episodes (Baia and Fondi di Baia) separated by a short time interval, and each characterized by several eruptive phases. Mineralogical, geochemical (major, and trace elements on whole rocks, major and volatile elements on matrix glasses, and melt inclusions), and Sr isotope characterization of the tephra material sampled along the entire sequence was carried out in order to constrain magmatic evolution and dynamics of the feeding system. Three main compositional groups were identified in matrix glasses and interpreted as representative of different magma bodies: (i) a trachyte (SiO2 60.3–64.7 wt.%), which is volumetrically predominant; (ii) a tephriphonolite-latite (SiO2: 55.1–57.9 wt.%); and (iii) an intermediate magma group between phonolite and trachyte compositions. This wide compositional heterogeneity contrasts with the narrow variability recognized in the bulk-rock compositions, which are all trachytic. Mineral, melt inclusions, and Sr isotope data suggest that the trachytic magma possibly derived from the Campanian Ignimbrite reservoir located at 6–9 km depth. Volatile content in matrix glass indicates a storage depth of at least 6 km for the tephriphonolite-latitic magma. The intermediate magma is interpreted as being derived from a remelting and assimilation process of a partially crystallized trachytic body (crystal mush) by the hotter tephriphonolite-latitic magma. As the tephriphonolite-latite was erupted together with the trachyte from the beginning of the eruption, we suggest that the ascent of this magma played a fundamental role in triggering the eruption. Upwards through the tephra sequence, we observed a progressive increase of the tephriphonolite-latitic and intermediate phonolite-trachytic components. The presence of banded clasts characterized by different compositions is also indicative of syn-eruptive mingling during the final phases of the eruption.

The marine isotope stage 1–5 cryptotephra record of Tenaghi Philippon, Greece: Towards a detailed tephrostratigraphic framework for the Eastern Mediterranean region

The iconic climate archive of Tenaghi Philippon (TP), NE Greece, allows the study of short-term palaeoclimatic and environmental change throughout the past 1.3 Ma. To provide high-quality age control for detailed palaeoclimate reconstructions based on the TP archive, (crypto)tephra studies of a peat core ‘TP-2005’ have been carried out for the 0–130 ka interval. The results show that the TP basin is ideally positioned to receive tephra fall from both the Italian and Aegean Arc volcanic provinces. Two visible tephra layers, the Santorini Cape Riva/Y-2 (c. 22 ka) and the Campanian Ignimbrite (CI)/Y-5 (c. 39.8 ka) tephras, and six primary cryptotephra layers, namely the early Holocene E1 tephra from the Aeolian Islands (c. 8.3 ka), the Campanian Y-3 (c. 29 ka) and X-6 tephras (c. 109.5 ka), as well as counterpart tephras TM-18-1d (c. 40.4 ka), TM-23-11 (c. 92.4 ka) and TM-33-1a (c. 116.7 ka) from the Lago Grande di Monticchio sequence (southern Italy), were identified along with repeatedly redeposited Y-2 and CI tephra material. Bayesian modelling of the ages of seven of the primary tephra layers, 60 radiocarbon measurements and 20 palynological control points have been applied to markedly improve the chronology of the TP archive. This revised chronology constrains the age of tephra TM-18-1d to 40.90–41.66 cal ka BP (95.4% range). Several tephra layers identified in the TP record form important isochrons for correlating this archive with other terrestrial (e.g., Lago Grande di Monticchio, Sulmona Basin and Lake Ohrid) and marine (e.g., Adriatic Sea core PRAD 1-2 and Aegean Sea core LC21) palaeoclimate records in the Mediterranean region.

Millennial-scale reworking of tephra in alluvial to shallow marine settings: Distinguishing pseudo-isochrons from genuine ones

Primary tephra layers can provide isochrons in a stratigraphic sequence. Such isochrons are powerful tools in terms of correlation and chronology of strata, and they constrain a chronological framework for geology, geomorphology, archaeology and palaeo-environmental studies in the Neogene to Quaternary. However, reworking processes can re-distribute tephra materials in both time and space, so that a given tephra can form a new discrete layer later in the depositional sequence, or it can be distributed in low concentrations (no visible layers, i.e., crypto-tephras) over a range of different stratigraphic horizons. The present study, based on sedimentological, petrographical, and geochemical analyses of reworked tephras in Japan, evaluates the duration and persistence of reworking and the tephra mobilisation and delivery to watersheds. Furthermore, it discusses how a unique isochron can be constructed from tephra distribution in a sedimentary sequence. Examples presented here are from fluvial and deltaic sequences in the Japanese Quaternary, which contain several visible tephra layers and a certain amount of tephra materials from multiple sources at different stratigraphical horizons. In the Niigata Plain, 5.4ka Numazawako tephra material continued to be reworked for more than 4000 years after the eruption of Numazawa volcano, and was re-deposited as reworked pumice grains consisting of a “visible” tephra layer in delta front deposits. Mixed tephra materials originating from an earlier eruption of Numazawa volcano and eruptions from other calderas were also identified. In the Tsugaru Plain, post-2.5ka subsurface deposits have >10% glass shards content throughout the sequence. Glass shards were derived from several different tephra materials, such as those from the most recent eruption of Towada volcano (AD 915), and earlier caldera forming eruptions (30 ka, 15ka). Some of the glass shards probably originated from erosion of exposed Pliocene pyroclastic bedrock. Thus, tephra reworking processes in alluvial to shallow marine settings can continue long after an eruption has ended, and can persist even during inter-eruptive (i.e., background sedimentation) periods. As tephra reworking involves complicated processes, careful observation and interpretations are necessary to evaluate whether tephra materials can truly provide an isochron for the strata in which they are found to exist.

Rock-magnetic signature of precipitation and extreme runoff events in south-eastern Patagonia since 51,200 cal BP from the sediments of Laguna Potrok Aike

A 106-m long sediment sequence from the maar lake Laguna Potrok Aike in southern Patagonia was recovered in the framework of the International Continental Scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO). About half of the sedimentary sequence is composed of mass movement deposits (MMDs) and the event-corrected record reaches back to 51,200 cal BP. Here we present a high-resolution rock-magnetic study revealing two sedimentary facies associated with MMDs and characterized by two different types of spurious gyroremanent magnetization (GRM) acquired during static alternating field demagnetization. The first rock-magnetic signature is detected in MMDs composed of reworked sand and tephra material. The signature consists of GRM acquired during demagnetization of the natural remanent magnetization (NRM) and other rock-magnetic properties typical of iron sulfides such as greigite. We interpret these intervals as authigenic formation of iron sulfides in suboxic conditions within the MMD. The second rock-magnetic signature consists of a series of 10 short intervals located on the top of MMDs characterized by GRM acquisition during demagnetization of the isothermal remanent magnetization (IRM). Based on geological, limnological, stratigraphic and climatic evidence these layers are interpreted as reflecting pedogenic hematite and/or goethite brought to the lake by runoff events related to precipitation and permafrost melt. The pedogenic iron minerals mobilized from the catchment most likely settled out of suspension on top of MMDs after a rapid remobilization event. The series of runoff events corresponds to periods of increased lacustrine productivity in Laguna Potrok Aike and are coeval within the limit of the chronology to warm periods of the Last Glacial as recorded in Antarctica, the deglaciation in the mid-latitudes of the Southern Hemisphere and enhanced precipitation during the Early Holocene in southeastern Patagonia.

Heavy-mineral analysis as a tool in tephrochronology, with an example from the La Sal Mountains, Utah, U.S.A.

Abstract An essentially pure tephra layer on a steep slope in the La Sal Mountains, Utah, U.S.A., is correlated with the 1.65 Ma old Guaje Tephra derived from the Jemez Mountains, New Mexico, U.S.A. The heavy-mineral contents and glass shards in sediments beneath the La Sal tephra layer indicate that tephra constituents are contained in deposits considerably older than the pure layer. This suggests that tephra material may become reworked while retaining its pure character, possibly due to laminar transport or to dislocation in a frozen condition. This raises the need to handle tephrochronological findings with great care.

Soil spatial variability of drainage properties in relation to phosphate retention and mineralogy on a river terrace of northern Manawatu, New Zealand

Spatial variability of soil drainage, topsoil phosphate retention (P-retention), and clay mineralogy were investigated in soils on a Manawatu river terrace developed from a mixture of loamy tephra, loess, and quartzo-feldspathic alluvial parent material. The cause of short-distance variation in soil drainage was investigated on an area of 60 ha from the Last Glacial river aggradation terrace (200–240 m a.s.l.). Three small window areas of 7.5 ha were then selected for grid sampling at 50-m centres within each of 3 map units with contrasting drainage class. Each of the window areas was found to contain 3–4 different drainage classes. Topsoil P-retention also varied (from 20 to 84%) within the window areas. We found a close relationship between soil drainage, P-retention, and clay mineralogy. Well-drained soils have high P-retention and the clay fraction contains 12–13% allophane. Poorly drained soils have low P-retention and the clay fraction has no allophane and contains mainly Kandite (Kaolinite and Halloysite). The short-distance variability in drainage is attributed to slight textural variations of the original alluvial parent material. This gives rise to the formation of different soil structures, which in turn influence the soil hydraulic conductivity and thence variable drainage properties, which influence the clay mineralogy and P-retention.

Wastewater Phosphorus Removal by Two Different Types of Andesitic Volcanic Tephra

Phosphorus (P) is the limiting nutrient controlling productivity in most inland freshwater systems. Several materials have been proposed for use to remove excess P from wastewater treatment, including volcanic lapilli and ash (tephra). There is limited data in using tephra as a P filter. There were two objectives of this study: 1) to determine the physical feasibility of tephra as a filter making sure the infiltration rate remains high enough to use under prolonged saturation, and 2) to test the suitability of volcanic tephra as a medium for removing P from an artificial solution on two different volcanic tephra materials: Okato and Papakai tephra. The experiment used a synthetic P influent solution (20.5 mg P/L) and a solution residence time in the columns of approximately 3 hours. By the end of the experiment infiltration in both tephras was adequate for use in wastewater treatment systems. The Okato tephra absorbed nearly 8 mg P/g tephra with 97% of the total amount of P added to the column over a 54 day period. The Papakai tephra absorbed only 4 mg P/g with a 52% of the total P added to the column.

Luminescence investigation of loess and tephra from Halfway House section, Central Alaska

Infrared stimulated luminescence (IRSL) properties of the Old Crow tephra and bracketing loess from the Halfway House site in Central Alaska are investigated in order to test newly developed techniques, including SAR and recently proposed fading corrections. Loess samples investigated show a standard growth of luminescence with regenerative dose while the tephra sample is less sensitive by an order of magnitude and saturates at lower dose. The growth curves obtained using multiple-aliquots regeneration (MAR) saturate at a higher value than those with the single-aliquot regeneration (SAR) protocol. Fading rate determinations for these samples are shown to be imprecise and no noticeable difference was observed between loess and tephra materials. Anomalous fading corrections using an average g value of 5% are applied to the natural test dose signal intensity using the dose rate correction (DRC) method. IRSL ages obtained for loess are in agreement with the expected age while the tephra age is lower than expected, suggesting the measured fading rate is underestimated for this material.

Tephrochronology of the 100 ka lacustrine sediment record of Lago Grande di Monticchio (southern Italy)

The results of a tephrochronological study on 340 distal tephra layers intercalated within 72.5 m of sediments in Lago Grande di Monticchio (southern Italy) are outlined. This maar lake provides a continuous, high temporal resolution record of climate and environmental change for the last 100 kyr. From a total of 340 intercalated tephra layers, 42 prominent tephras have been selected for detailed microscopic, chemical and chronological investigations in order to obtain a second chronological fundament complementary to the varve-supported sedimentation rate chronology providing in combination a high precision timescale of this important palaeoclimatic record. All these tephra layers have been correlated with highly explosive eruptions of Central and South Italian volcanoes. The historically dates, radiometric, radioisotopic and interpolated ages of 26 correlated tephra events and direct laser 40Ar/ 39Ar dates for Monticchio tephra layers are consistent with ages of tephra deposition provided by the independent sedimentation rate chronology of Monticchio sediments with a mean deviation of ∼5%. Aside from its tephrochronological purpose, the study of tephra layers in the Monticchio sediments also contributes to a better knowledge of the explosive history of Italian volcanoes and the dispersal of erupted tephra material.

Volcanic soils of Iceland

The parent materials of all Icelandic soils are volcanic in origin, and most of the soils are classified as Andosols. Iceland has the largest area of Andosols in Europe, and may have >5% of all Andosols in the world. A new classification scheme based on the World Reference Base (World Reference Base for Soil Resources. World Soil Resources Reports 84, FAO, Rome) is used to provide an overview of Icelandic volcanic soils. The data were acquired as part of a recently initiated effort to build a database for Icelandic soils, but are also partly based on data from the EU COST-622 action, a literature review and unpublished Icelandic research. The main soil types in Iceland are Histosols, Histic Andosols, Gleyic Andosols, Brown Andosols, Vitrisols and Leptosols. In the Icelandic language, a single term is used to refer to each soil type. This system reflects the dominant influence of eolian deposition and drainage conditions on the formation of Histosols and Andosols. The parent materials of Icelandic soils are mixtures of tephra layers and eolian sediments consisting mostly of volcanic glass. The steady flux of eolian sediments from unstable sandy deserts constantly recharges the surface with basaltic tephra materials. The Histosols (>20% C) have appreciable amounts of andic materials because of the eolian deposition. The Andosols (Histic, Gleyic and Brown Andosols) show characteristic properties of soils dominated by andic materials with allophane contents of up to 30%. Ferrihydrite commonly accounts for 5–15% of the soil. The contents of both allophane and ferrihydrite generally decrease with increasing organic C content of soil horizons, as organic matter inhibits allophane formation and iron tends to become reduced and lost in poorly drained locations. The Vitrisols are soils of desert surfaces with low organic content, but they usually meet criteria for andic materials with >30% glass and (Al+1/2Fe) o>0.4%. Cryoturbation is intense in Iceland, resulting in a range of geomorphic surface features. The cryoturbation is related to both climatic factors and the andic soil properties including high water retention and rapid hydraulic conductivity.

Andisols of Deserts in Iceland

Desert areas cover 35 to 45000 km2 of Iceland or about 35 to 45% of the country. These surfaces have very low vegetation cover as a result of several environmental factors and anthropogenic impacts. A good understanding of the soils of the deserts is a key factor for successful restoration of these ecosystems. Very limited data has previously been published about the soils of Icelandic deserts and limited research has been reported on soils that form in basaltic tephra materials under similar conditions elsewhere in the world. The purpose of the research reported here was to gain a basic understanding of properties, variability, and classification of the soils of Icelandic deserts. Eight soil pedons, representing a variety of desert surfaces, were described, sampled, and analyzed for key physical and chemical properties. The morphology was generally characterized by a frost‐heaved gravel layer at the surface, with finer subsurface horizons with abundance of volcanic glass. The soils had low organic content (&lt;10 g kg−1), and very low levels of N. Water holding capacity was generally &lt;50 g kg−1 at 1.5 MPa. Phosphorus retention is 24 to 93% in A and B horizons. The soils were near neutral in reaction but the pH in NaF solution was commonly around 10. Mineralogy was dominated by volcanic glass, but allophane and ferrihydrite are also present. The results of this study show that most Icelandic deserts soils are Typic Virtricryands according to soil taxonomy. Icelandic Andisols combined are 5 to 7% of the world's Andisols.

Andisols from Four Different Regions of Iceland

AbstractLimited information has been published on Andisols in Iceland, but such data are important for understanding the erosional and periglacial processes that are intense in Iceland. The objectives of this research were to investigate Andisols that developed in tephra and eolian materials and that are highly susceptible to soil erosion, and to evaluate the effectiveness of the recently established Andisol order for providing meaningful classes in Iceland. Four soils that formed in 1‐ to 3‐m‐thick tephra and eolian materials of various origins were studied. The soils have low bulk density (&lt;0.8 g cm−3), high −0.033 and −1.5 MPa water retention (0.27–1.18 and 0.17–0.85 kg kg−1, respectively, excluding tephra horizons), and Atterberg limits characteristic of field‐moist Andisols (plastic limits of 0.49–0.95 kg kg−1 and liquid limits of 0.54–0.97 kg kg−1). Soil reaction (H2O) ranges between pH 5.6 and 6.7. Organic C contents are high but erratic; they range from 21 to 90 g kg−1, excluding thick tephra horizons that are characteristically low in C. Soil color was not related to organic C content. The cation‐exchange capacity is generally high (22–46 cmolc kg−1) and is highly related to organic C, oxalate‐extractable Al + Fe, and precipitation (R2 = 0.92). The &lt;0.002‐mm fraction is dominated by allophone and ferrihydrite represented by high oxalate‐extractable Al, Fe, and Si. High organic C content was not found to inhibit allophone formation in surface horizons. These Andisols developed from sediments of complex history consisting of tephra layers deposited during episodic volcanic events that are interstratified with eolian polycycled materials of glacial‐fluvial and andic origin. Assigning buried horizons and lithological discontinuities was difficult and often arbitrary and was not done for the eolian and tephra materials. All the pedons were classified as Haplocryands. More than 60 000 km2 of Andisols may occur in Iceland, which would constitute 5 to 6% of all Andisols in the world.

Clay minerals of four soils formed in eolian and tephra materials in Iceland

Clay minerals in a Vitricryand and three Haplocryands derived from eolian and tephra materials in different parts of Iceland and in glacial till samples representative of underlying strata were studied by a combination of methods. The soils are primarily used as rangelands and are highly susceptible to wind erosion. Allophanes, imogolite and poorly-crystalline ferrihydrite are abundant (> 700 g/kg of the clay) throughout the soils, including A horizons. This clay mineralogy would give rise to stable, low-density aggregates that influence the susceptibility of the soils to wind erosion. It also affects chemical properties such as high phosphate retention of the soils, even of the Cryands with relatively low clay contents (160–275 g/kg). Imogolite was found in some but not all horizons of all soils. No particular relationship of imogolite to measured Si/Al molar ratios of the oxalate-oxalic acid soluble fractions of the clays (0.51 to 1.13) was evident. Layer silicate minerals and laminar opaline silicas are either not present or occur in small quantities. Plagioclase, augite and/or their weathering residues were found in the clay and silt separates. Dark-colored glass is predominant in the fine sand throughout the soils and the tills. One till sample had a clay mineral composition similar to the eolian-andic soils, while the other contained smectite and possibly a spherical halloysite-smectite intermediate, but not allophane and imogolite, as major weathering products. The clay mineral composition of these soils and tills was compared with those derived from basic tephras in other regions.